Aircraft systems include various types of rotating electrical machines, such as alternating current (AC) motors and generators of various designs. Generally, an AC machine includes a rotor and a stator. If the machine is operated as a motor, electrical power is supplied to the stator to develop a rotating electrical field. This rotating electrical field generates a torque in the rotor causing it to rotate. If the machine is operated as a generator, electrical power is supplied to the rotor to generate a magnetic field. A prime mover is coupled to the rotor causing it, and thus the generated magnetic field, to rotate. This rotating magnetic field induces a voltage into the stator, which supplies electrical power to a load.
A stator for AC machines may typically include a stator core having a plurality of wire coils wound around it. The stator core is generally formed by laminating a plurality of ring plates. The ring plates include an inner circumference that together form a main axial opening through the stator core for housing rotating components. A plurality of slots is formed in the inner circumference, and each of the slots extends along the axis of the main axial opening. Each slot includes an axial slit that allows communication between the slot and the main axial opening. The wire coils typically include ends that are inserted into the slots.
The wire coils may produce heat during machine operation and may, consequently, undesirably transfer the heat to the core. To prevent such a consequence, thermal insulating and/or cooling schemes are typically included in AC machines. In one example, a portion of each coil is wrapped with a thermally insulating liner that isolates coils from the stator core, and inhibits heat transfer to the core. Although this is adequate for small rotating machines, it typically does not sufficiently inhibit heat transfer in rotating machines that include larger sized cores. In other examples, cooling fluid or gas is directed into the stator slots and contacted with the coils. However, because the slots are typically designed to open into the main axial opening, the fluid or gas may leak through the opening and contact the rotating components causing the components to become inoperable.
Hence, there is a need for a cost-efficient, effective system for cooling an electrical rotating machine of any size. Additionally, it is desirable for the system to be capable of being retrofitted into existing electrical rotating machines. Moreover, it is desirable for the system to operate without affecting the rotating components of the machine.